The second annual World Science Festival, a five-day extravaganza of performances, debates, celebrations and demonstrations, including an all-day street fair on Sunday in Washington Square Park, began with a star-studded gala tribute to the Harvard biologist Edward O. Wilson at Lincoln Center Wednesday night. Over the next three days the curious will have to make painful choices: attend an investigation of the effects of music on the brain with a performance by Bobby McFerrin, or join a quest for a long-lost mural by Leonardo Da Vinci at the Metropolitan Museum of Art? Learn about the science behind “Battlestar Galactica” with actors from the show, or head to one of various panels of scientists and philosophers arguing about free will, alternate universes, science and religion, time and what it means to be human?

On Saturday there’s a chance to play naturalist, scouring a pair of New York parks under professional guidance in what Dr. Wilson calls a “BioBlitz” for flora, fauna and “all things crawly.” On Sunday you can get your hands in a variety of experiments at the street fair, including a “CSI”-style crime scene.

The festival is the brainchild of Brian Greene, a Columbia University physicist and mathematician and best-selling author, and his wife, Tracy Day, a former producer for ABC. They say they thought of the project after attending a science festival in Genoa, Italy, and being impressed by seeing science bubbling through the streets and cafes.

The idea is to mix up art, theater and music with the inevitable talking heads and professional interlocutors like Charlie Rose or Alan Alda, who can keep the discussion moving and down to earth, in order to entice an audience that didn’t know it was interested in science. Ms. Day likes to describe the strategy this way: “Bring them in for the art and have them leave with science.”

Last year more than 100,000 people stood in block-long lines to watch dancers reinterpret string theory, Oliver Sacks interpret his own failing eyesight, scientists debate quantum mechanics and what it means to be human. There were about 46 events, including a daylong street fair in Washington Square Park. In the end everything sold out, the organizers said.

“We learned that there is an untapped hunger in the public for a way into science.” said Dr. Greene, who recently sat down with Mr. Alda (who was accompanied by a ghost Twitterer), to discuss the festival.

Mr. Alda, perhaps best known as Hawkeye Pierce in “M*A*S*H,” is also longtime science buff and admits to wanting to be an inventor as a boy. Asked about the famous cultural divide between art and science he said that they are mutually reinforcing: “Art needs rigor, and science needs creativity.”

In a sort of smackdown between the two, art, represented by Mr. Alda, got the better of science, represented by Dr. Greene. Challenged to explain string theory, Mr. Alda produced a serviceable explanation: the smallest entities in nature are wriggling strings that take on different identities depending on how they vibrate. But Dr. Greene was stumped when asked to hum the theme song from “M*A*S*H.”

This year, because of the leaner economic climate, the festival offerings have been scaled back a bit to 40 events, including the street fair on Sunday in Washington Square Park. Ticket prices have also been reduced, Dr. Greene said. (Information on family activities: Spare Times, Page 24.)

The festival is sponsored by 18 organizations, including the Simons Foundation, the Alfred P. Sloan Foundation and the John Templeton Foundation.

One of the biggest differences this year, Dr. Greene said, was symbolized by Wednesday night’s gala in honor of Dr. Wilson. In addition to celebrating science, Dr. Greene explained, “we also need to celebrate great scientists — people who’ve profoundly changed our lives but are often barely known.”

He said that future editions of the festival would feature other scientists: “When kids look up to great scientists the way they do to great musicians and actors, civilization will jump to the next level.”

Dr. Wilson, an expert and lover of ants, certainly qualifies. He has spent his career taking seriously the notion that the behavior of creatures is just as much a part of nature as hair color or cholesterol counts and so founded the field known as sociobiology. For his troubles he has won two Pulitzer prizes and had a pitcher of water dumped on his head by political activists worried about the implications of his work for human societies.

Dr. Wilson’s imprint on this year’s festival extends beyond the opening gala and a dramatization of his life on Thursday by the actress Anna Deavere Smith. He will also be featured Friday night on a panel discussing what it means to be human. The topic this year will focus on altruism, a problem that has engaged many evolutionary biologists and philosophers over the years. On Sunday night Dr. Wilson will give a talk on his adventures “BioBlitzing” the world in search of new species.

On Wednesday, speaking at a rapturous reception after his birthday gala, Dr. Wilson called attention to what he called a lopsided emphasis in the current movement toward all things green on preserving the physical environment. More emphasis, he said, needs to be put on preserving the diverse forms of life on this planet, which are dying out at a shocking rate. If we devote ourselves to saving them, we will automatically fix the environment, he said.